Photographic shortstop compositions



2,980,536 PHOTOGRAPHIC SHORTSTOP COMPOSITIONS No Drawing. Filed July 2, 1956, Ser. No. 595,052 Claims. (Cl. 96-62) This invention relates to new and improved photographic shortstop compositions. More particularly, this invention relates to new and improved strong acid photographic shortstop baths. In one specific aspect thereof, this invention relates to new and improved rapid acting photographic shortstop baths.

As is well known, only a small portion of the silver halides present in photographic emulsions is actually utilized in the exposure .and development of negatives and prints. Afterdevelopment isv complete it is necessary to remove the excess silver halide in Order to pro duce a permanent negative or print. The process of removing this excess silver halide is termed fixing and usually involves treatment of the developed negative or print with a solution containing a material capable of forming a Water soluble complex with silver halides. Sodium thiosulfate pentahydrate (hypo) and ammonium thiosulfate (Thiamate) are the, most commonly used fixing agents, the aqueous fixing bath usually containing, in addition to one or both of the fixing agents named, an emulsion hardening ingredient such as alum. Fixing baths conventionally exhibit an acidic reaction.

An aqueous solution of a suitable organic reducing agent or mixture thereof is usually employed in the development of negatives and prints, the developments bath conventionally containing a large amount of sodium sulfite and conventionally exhibiting an alkaline reaction.

It is obvious that the direct transfer of developed neg atives or prints from the developer solution to the fixing bath results in contamination of the latter due to the car- "ry-over of developer held on the surfaces and absorbed by the emulsion of the developed negatives and prints. This contamination results in the rapid exhaustion of the fixing baths due to the neutralization thereof by the alkaline developer. Developer contamination of the fixing bath also brings'about precipitation or sludging out of a portion of the alum hardener-in'the fixing bath which results in reduction or destruction of the emulsion hardening properties of the bath and frequently in .defective finished negatives and prints due to the inclusion of particles of the precipitated sludge by the emulsion.

To avoid the difficulties set forth above it has been common practice to subject developed negatives and prints to a water wash prior to their transfer to the fixing bath. This procedure is entirely satisfactory if a relatively inactive developer has been employed and the time of development is not particularly critical. However, it is obvious that the removal of developer absorbed by the emulsion through use of a water wash is a comparatively slow process, requiring the diffusion of the water into the emulsion and the displacement of the absorbed United States Patent "0 quality.

7 Patented Apr. 18, 1961 "ice developer thereby. During all this time the developer present in the emulsion continues toact upon the silver halides and accordingly this water wash process can only be employed if the developer is slow acting and the development time is not particularly critical.

Due to continuing pressures for greater speed in the finishing of exposed negatives and prints, developing baths of higher and higher activity are being employed and with these a water wash following development and prior to fixing is entirely unsatisfactory. The removal of absorbed rapid developers by a water wash is so slow that control of the extent of development is impossible. To overcome this difficulty, it has been common practice to immerse negatives and prints that have been processed in an active development bath in a shortstop bath prior to transfer, to the fixing bath. Such shortstop baths conventionally consist of a dilute (1-5%) aqueous solution of acetic acid. This solution, on diffusing into the emulsion, neutralizes the alkalinity of the absorbed developer, therebydestroying thereducing (developing) action thereof. Such shortstop solutions are adequate when used in connection with active developers.

Normally, it is desirable to process exposed negatives and prints in the shortest possible time consistent with the production of finished negatives and prints of satisfactory In many fields (for example, certain military and medical applications ofphotography, photofinishes, certain types of theater screen television presentations, et cetera) extreme speed in processing is essential. To reduce processing times'to a minimum, superactive developers are being increasingly employed and shortstop baths consisting of dilute aqueous solutions of acetic acid are unsatisfactory for use in connection with such developers. Acetic acid is weakly ionized, a 3% aqueous solution thereof having a pH of about 2.5. In addition, sodium acetate, resulting from the neutralization of the alkalinity of the developer by acetic acid, acts as a buffer and further reduces the ionization of the weakly ionized acetic acid remaining after neutralization so the maximum degree of acidity that can be obtained is that represented by a pH appreciably above 2.5. This acidity is not sufficient- 1y high to destroy the action of such superactive developers with the speed necessary to provide a development process that is under complete control.

Accordingly, when such superactive developers are employed, it is conventional to use a dilute aqueous solution of a strong acid, such as sulfuric acid or hydrochloric acid, as a shortstop bath. A 2% solution of sulfuric acid has a pH of about 1.0. Such shortstop solutions comprising a dilute aqueous solution of a strong acid destroy the activity of superactive developers quickly and completely and the highly ionized sodium salt produced by the neutralization of the alkalinity of the developer has no great effect on the ionization of the excess highly ionized acid so that the maximum degree of acidity furnished by such strong acid shortstop solutions is about that represented by a pH of 1.0.

Dilute sulfuric acid solutions are conventionally employed as strong acid shortstop baths for use in connection with superactive developers. However, due to the potential hazards involved in the transportation and use of sulfuric acid and the difficulty in measuring the small amount of sulfuric acid required to give a shortstop bath of the proper acidity, it is common practice to use sodium bisulfate (usually in the form of sodium bisul fate monm 3 hydrate) as the source of the sulfuric acid. A solution containing 57 g. sodium bisulfate monohydrate per liter is equivalent to a 2% sulfuric acid solution.

A very serious objection to the use of strong acid shortstop baths has been their tendency to decompose the sulfites of the developer, carried to the shortstop bath by the developed negatives and prints, with the evolution of sulfur dioxide. This sulfur dioxide is not only irritating to the operator but also brings about the corrosion of metallic objects (tanks, trays, et cetera) in the darkroom. We have discovered that the evolution of sulfur dioxide during the employment of strong acid shortstop baths can be eliminated by incorporation of an aldehyde or ketone, such as formaldehyde, .paraformaldehyde, acetone, methyl ethyl ketone, glyoxal, and the like therein. We have found that to achieve elimination of sulfur di oxide evolution during the employment of strong acid shortstop baths, the selected aldehyde or ketone must be present therein in an amount suflicient to give a carbonyl function concentration of at least four grams per liter. With such aldehydes as formaldehyde and paraforrnaldehyde and, more especially, glyoxal, the weight of the carbonyl group or groups present is very nearly the same as the weight of the aidehydes (on a 100% basis) but with ketones and higher molecular weight aldehydes there is a considerable difference between the weight of the compound and the weight of carbonyl function it contains. Thus, methyl ethyl ketone (molecular weight, 72) contains only some 39% by weight of the carbonyl group so the strong acid shortstop baths of our invention require about g. per liter of this ketone to produce a carbonyl function concentration of 'four grams per liter.

One object of this invention is to provide 'an improved strong acid shortstop composition.

Another object ofthis invention is to provide a method for the rapid termination of the development of photographic negatives and prints without simultaneous evolution of gaseous 'sulfurdioxide.

A further object of this invention is to providean improved strong acid shortstop composition that does not evolve gaseous sulfur dioxide during the employment thereof. I

Additional objects of this invention will become ap parent as the descriptionthe'r'eof proceeds. V

For the better understanding of'tliis invention, the following examples set forth complete descriptions of specific embodiments thereof. It is to be understood that these specific embodiments are illtistrativ'e only and are not to be considered as limitations on the spirit or scope of the invention.

Example 1 Strong acid shortstop solutions of this invention and having an acidity equivalent to that of a dilute aqueous solution containing from 1% to 5% sulfuric .acid by Weight may be prepared as follows: i

From 30 g. to 140 g. sodium bisulfate monohydrate (depending upon the equivalent sulfuric acid acidity desired) are dissolved in about 800 cc. water following which from ll) cc. to 40 cc. of a 30% aqueous solution of glyoxal are added thereto, sufficient additional water then being added to theresulting solution togive a final volume of one liter. The following factors, among others, are to be considered milking the respective quantities of sodium bi sulfate nion'ohydrate and glyoxal solution to be employed AK in making a specific improved strong acid shortstop solution in accordance with this invention:

The quantity of sodium bisulfate monohydrate to be employed is determined by considering the alkalinity of the developer to be used in connection therewith in conjunction with the capacity desired of the strong acid shortstop solution. The amount of developer carried over to the shortstop solution is essentially directly proportional to the area of the developed negatives or prints transferred thereto, other conditions being constant. With a superactive developer, strong acid shortstop solutions become too sluggish for satisfactory control of the high speed developing process after the pH of the shortstop solution has increased to about 2.0 to 2.5 as the result of neutralizing the alkalinity of developer solution transferred to the shortstop solution. Such superactive developers are usually strongly alkaline and as a result, unless the strong acid short stop baths have a comparatively high acid content they soon become exhausted when used in connection with such developers. A commercially acceptable capacity for strong acid shortstop baths can be set, somewhat arbitrarily, and the acid content of a bath that will achieve this standard capacity can be determined on the basis of the alkalinity of the developer to be used in connection therewith. As a specific example of the interrelation of these various factors, if it is desired that one liter of strong acid shortstop solution stop develop! ment of at least twenty developed and transferred eight by ten inch film negatives with suflicient speed to give s'a'tisfact'ory' controlofthedevelopment process when a Wide ly used superactive developer of high alkalinity isemployed, then the strong acid short stop bath should contain about g. per liter sodium bisulfa'te monohydr-ate,

' or an equivalent sulfuric acid acidity of about 3.5%. If

desired, a lesser amount of sodium bisulfate mon'ohydrate may be used, for example, 30 g. perliter, but'obviously this will result in a shortstop solution having a much lower capacity. O'r, up to g. per liter of the'sodiu'm bisulfate monohydrate may be employed to give a shortstop solution of even higher capacity. 7

It is evident from the above that the capacity of the strong acid shortstop solutions of this invention may 'be varied at will over a considerable range and the actual capacity of such solutions is largely determined by considerations of commercial acceptability.

The concentration of g'lyoxal in the strongia'cid shortstop solutions is determined by the concentration of sulfites in the developer. If the saline content of the developer is low onl a small quantityio ffglyoxal "is required while if the sulfit'e concentration of the developer is high a greater concentration of glyox'al should be present. For obvious reasons, the concentration of glyox'al and the capacity (that is the acid content) of the'shortstop solutions of this invention should be so interrelated that no sulfur dioxide is evolved during the active life of the shortstop solution. In the specific example previously given, a strong acid shortstop solution. containing 100 g. of sodium bisulfate monohydr ate per liter when employed in connection "with a widely used superactive developer of high alkalinity had a capacity of twenty developed eight by ten inchfilm negatives per liter. This particular developer contained 50 g. sodium sulfite per liter and it was found that the strong .acid shor'tstopsolution required about 20 cc. of 30% glyoxal solution per liter to prevent the evolution of sulfur dioxide during the shor-tstopping of'these-tw'enty eight by teninch developed filmnegatives.

Part or all of thesodium bisulfate monohydrateof the compositions of the .presentexample maybe replaced by chemically equivalent amounts of ammonium bisulfate, potassium 'bisulfate or mixtures thereof. Part or all of the acid requirements may also be :supplied through use of sulfuric acid, hydrochloric acid or similar strong mineral acids.

- I ExampleZ bisulfate monohydrate and of aldehyde are also applicable here and the sodium bisulfate monohydrate may be replaced, in part or entirely, by the alternates set forthin the previous example. Also, the formaldehyde of the present example may be replaced, in part or entirely, by equivalent amounts of paraformaldehyde.

Example 3 Strong acid shortstop solutions of this invention having an acidity equivalent to from 1 to 5% sulfuric acid may be prepared as follows:

From 30 to 140 g. sodiumbisulfate monohydrate are dissolved in about 800 cc. water and to 80 cc. acetone are added thereto, thenecessary additional water then being added to the resulting solution to give a final total volume of one liter.

The considerations previously given under Example 1 with respect to suitable specific quantities of sodium bisulfate monohydrate and of the carbonyl function are also applicable here and the sodium bisulfate monohydrate may be replaced, in part or entirely, by the alternates set forth in Example 1.

Example 4 Strong acid shortstop solutions of this invention containing from 1 to 3% hydrochloric acid may be prepared as follows:

From 22.5 to 68 cc. of 37.5% hydrochloric acid are added to about 800 cc. water following which about one gram of potassium chloride per cubic centimeter hydrochloric acid employed is dissolved therein. From 10 to 40 cc. of 37% formaldehyde solution are added to the resulting solution which is then brought to a volume of one liter by the addition of the necessary quantity of water. The considerations previously given under Example 1 with respect to suitable acid concentrations of the final solution and the aldehyde content thereof are also applicable here and the formaldehyde may be replaced, in part or entirely, with paraformaldehyde.

Be it remembered, that while this invention has been described in connection with specific details and specific embodiments thereof, these details and embodiments are illustrative only and are not to be considered limitations on the spirit or scope of said invention except in so far as these may be incorporated in the appended claims.

We claim:

1. In the process of rapidly producing a silver image in a light exposed silver halide emulsion layer comprising (1) developing the exposed emulsion layer with a superactive black-and-whitedeveloper, (2) shortstopping the development by immersing the developed emulsion layer in an aqueous solution of a substance selected from the group consisting of sodium bisulfate, potassium bisulfate, ammonium bisulfate, sulfuric acid and hydrochloric acid having an acid hydrogen content equivalent to that of an aqueous solution containing from about 1% to about 5% by weightsulfuric acid and having a pH of not more than 2.0, and (3) fixing the developed emulsion layer, the improvement comprising shortstopping the development with an aqueous shortstop solution of the previously specified composition and acidity and containing, in addition, a substance selected from the group consisting of formaldehyde, paraformaldehyde, glyoxal, acetone and methyl ethyl ketone in an amount sufiicient to produce a carbonyl function concentration therein of from about 4 to about 32 grams per liter.

2. In the process of rapidly producing a silver image in a light exposed silver halide emulsion layer comprising (1) developing the exposed emulsion layer with a superactive black-and-white developer, (2) shortstopping the development by immersing the developed emulsion layer in an aqueous solution of a substance selected from the group consisting of sodium bisulfate, potassium bisulfate, ammonium bisulfate, sulfuric acid and hydrochloric acid having an acid hydrogen content equivalent to that of an aqueous solution containing from about 1% to about 5% by weight sulfuric acid and having a pH of not more than 2.0, and (3) fixing the developed emulsion layer, the improvement comprising shortstopping the development with an aqueous shortstop solution of the previously specified composition and acidity and containing, in addition, glyoxal in an amount sufiicient to produce a carbonyl function concentration therein of from about 4 to about 32 grams per liter.

3. In the process of rapidly producing a silver image in a light exposed silver halide emulsion layer comprising (1) developing the exposed emulsion layer with a superactive black-and-white developer, (2) shortstopping the development by immersing the developed emulsion layer in an aqueous solution of a substance selected from the group consisting of sodium bisulfate, potassium bisulfate, ammonium bisulfate, sulfuric acid and hydrochloric acid having an acid hydrogen content equivalent to that of an aqueous solution containing from about 1% to about 5% by weight sulfuric acid and having a pH of not more than 2.0, and (3) fixing the developed emulsion layer, the improvement comprising shortstopping the development with an aqueous shortstop solution of the previously specified composition and acidity and containing, in addition, formaldehyde in an amount sufiicient to produce a carbonyl function concentration therein of from about 4 to about 32 grams per liter.

4. In the process of rapidly producing a silver image in a light exposed silver halide emulsion layer comprising (1) developing the exposed emulsion layer with a superactive black-and-white developer, (2) shortstopping the development by immersing the developed emulsion layer in an aqueous solution of a substance selected from the group consisting of sodium bisulfate, potassium bisulfate, ammonium bisulfate, sulfuric acid and hydrochloric acid having an acid hydrogen content equivalent to that of an aqueous solution containing from about 1% to about 5% by weight sulfuric acid and having a pH of not more than 2.0, and (3) fixing'the developed emulsion layer, the improvement comprising shortstopping the development with an aqueous shortstop solution of the previously specified composition and acidity and containing, in addition, paraformaldehyde in an amount sufiicient to produce a carbonyl function concentration therein of from about 4 to about 32 grams per liter.

5. In the process of rapidly producing a silver image in a light exposed silver halide emulsion layer comprising (1) developing the exposed emulsion layer with a superactive black-and-white developer, (2) shortstopping the development by immersing the developed emulsion layer in an aqueous solution of a substance selected from the group consisting of sodium bisulfate, potassium bisulfate, ammonium bisulfate, sulfuric acid and hydrochloric acid having an acid hydrogen content equivalent to that of an aqueous solution containing from about 1% to about 5% by weight sulfuric acid and having a pH of not more than 2.0, and (3) fixing the developed emulsion layer, the improvement comprising shortstopping the development with an aqueous short- 4 stop solution of the previously specified composition and therein of from about 4 to about 32 grams per liter.

References Cited in the file of this patent UNITED STATES PATENTS Wormell et al Sept. 25, 1945 Cline Oct. 15, 1946 8 Harsh et al July 19, 1949 Bates Oct. 27, 1953 Andreyev Mar. 18, 1958 OTHER REFERENCES Walker: Formaldehyde, Second Edition, Monograph Series #120, Reinhold Pub. Co., NY. (1953), p. 168. Clerc: Photography Theory and Practice, Second 7 10 Edition, Greenwood and Co., London, England (1937), Royler et a1 June 17, 1947 pp. 238-239. 

1. IN THE PROCESS OF RAPDILY PRODUCING A SILVER IMAGE IN A LIGHT EXPOSED SILVER HALIDE EMULSION LAYER COMPRISING (1) DEVELOPING THE EXPOSED EMULSION LAYER WITH A SUPERACTIVE BLACK-AND WHITE DEVELOPER, (2) SHORTSTOPPING THE DEVELOPMENT BY IMMERSING THE DEVELOPED EMULSION LAYER IN AN AQUEOUS SOLUTION OF A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF SODIUM BISULFATE, POTASSIUM BISULFATE, AMMONIUM BISULFATE, SULFURIC ACID AND HYDROCHLORIC ACID HAVING AN ACID HYDROGEN CONTENT EQUIVALENT TO THAT OF AN AQUEOUS SOLUTION CONTAINING FROM ABOUT 1% TO ABOUT 5% BY WEIGHT SULFURIC ACID AND HAVING A PH OF NOT MORE THAN 2.0, AND (3) FIXING THE DEVELOP EMULSION LAYER, THE IMPROVEMENT COMPRISING SHORTSTOPPING THE DEVELOPMENT WITH AN AQUEOUS SHORTSTOP SOLUTION OF THE PREVIOUSLY SPECIFIED COMPOSITION AND ACIDITY AND CONTAINING, IN ADDITION, A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF FORMALDEHYDE, PARAFORMALDEHYDE, GLYOXAL, ACETONE AND METHYL ETHYL KETONE IN AN AMOUNT SUFFICIENT TO PRODUCE A CARBONYL FUNCTION CONCENTRATION THEREIN OF FROM ABOUT 4 TO ABOUT 32 GRAMS PER LITER. 